Test strips are often used to measure the presence and/or concentrations of selected analytes in test samples. For example, a variety of test strips are used to measure glucose concentrations in blood to monitor the blood sugar level of people with diabetes. These test strips include a reaction chamber into which a reagent composition has been deposited. Current trends in test strips require smaller test samples and faster analysis times. This provides a significant benefit to the patient, allowing the use of smaller blood samples that can be obtained from less sensitive areas of the body. Additionally, faster test times and more accurate results enable patients to better control their blood sugar level.
In connection with smaller sample volumes, it is known to provide test strips having a sufficiently small reaction chamber such that sample fluid is drawn therein by capillary action, which is a phenomenon resulting from the surface tension of the sample fluid and the thermodynamic tendency of a liquid to minimize its surface area. For example, U.S. Pat. No. 5,141,868 discloses a test strip having a cavity sized sufficiently small to draw sample liquid therein by capillary action. The cavity is defined by two parallel plates spaced about 1 mm apart by two epoxy strips extending lengthwise along lateral sides of the plates. The cavity is open at both ends, one of which receives the sample, and the other of which allows air to escape. The cavity includes an electrode structure and carries a coating of a material appropriate to the test to be performed by the test strip.
Various other test strip designs include capillary cavities that draw sample fluid therein and include vent openings to allow air to escape. Typically, the vent opening is punched or otherwise formed in either the top or bottom film that forms the sample receiving cavity. Manufacturing issues arise because of the need to precisely locate the vent hole relative to the cavity. For example, if the cavity is centrally disposed lengthwise within the test strip, a vent hole aligned left or right of center may not connect or communicate with the cavity. Since the strips are typically mass-produced from a continuous web, an error in alignment of the vent hole can affect hundreds or even thousands of test strips.
Moreover, punching a hole for the vent opening requires a separate process step and a cutting die or other equipment to form the opening. In view of cavity sizes becoming increasingly smaller in modern test strips, forming the vent opening has become a more delicate process step. It would be desirable to reduce the potential for error and to reduce the costs associated with forming the vent opening in test strips requiring the same.